The present invention generally relates to crimped multicomponent nonwoven fabrics and methods of making the same.
Nonwoven webs of continuous thermoplastic polymer fibers made by melt-spinning thermoplastic polymers are known in the art. As examples, melt-spun fiber webs or spunbond fiber webs are described in U.S. Pat. No. 4,692,618 to Dorschner et al., U.S. Pat. No. 4,340,563 to Appel et al. and U.S. Pat. No. 3,802,817 to Matsuki et al. In addition, multicomponent spunbond fibers have likewise been made heretofore. The term xe2x80x9cmulticomponentxe2x80x9d refers to fibers formed from at least two polymer streams that have been spun together to form one fiber. Multicomponent fibers comprise fibers having two or more distinct components arranged in substantially constantly positioned distinct zones across the cross-section of the fibers that extend substantially continuously along the length of the fibers. Multicomponent fibers and methods of making the same are known in the art and, by way of example, are generally described in U.S. Pat. No. 5,108,820 to Kaneko et al., U.S. Pat. No. 5,382,400 to Pike et al., U.S. Pat. No. 5,277,976 to Hogle et al., U.S. Pat. No. 5,466,410 to Hills and U.S. Pat. No. 3,423,266 and 3,595,731 both to Davies et al.
The characteristics or physical properties of such nonwoven webs are controlled, at least in part, by the density or openness of the fabric. The web density can be controlled to a great deal by the fiber structure and, in particular, by the curl or crimp of a fiber along its length. Generally speaking, nonwoven webs made from crimped fibers have a lower density, higher-loft and improved resiliency compared to similar spunbond fiber nonwoven webs of uncrimped fibers. Accordingly, various crimped fiber nonwoven webs, and in particular nonwoven webs of crimped multicomponent spunbond fibers, have heretofore been made that have excellent physical characteristics such as good hand, strength and loft.
Various methods of crimping melt-spun fibers are known in the art. For example, it is known in the art to induce fiber crimp with heat such as described in U.S. Pat. No. 4,068,036 to Stanistreet and U.S. Pat. No. 5,382,400 to Pike et al. In addition, PCT Application US97/10717 (publication no. WO 97/49848) discloses a method of forming self-crimping multicomponent spunbond fibers utilizing a polyolefin component and a non-polyurethane elastic block copolymer component such as copolyesters, polyamide polyether block copolymers and A-B or A-B-A block copolymers with a styrenic moiety. These fibers crimp by simply drawing the molten fibers and thereafter releasing the attenuating force; no post-treatment steps are required to induce crimp. In addition, U.S. Pat. No. 5,876,840 to Ning et al. teaches spunbond multicomponent fibers having a non-ionic surfactant additive within one of the components in order to accelerate its solidification rate. By adding the non-ionic surfactant to one of the components of the multicomponent fiber it is possible to develop and activate a latent crimp by drawing with unheated air.
The use of a subsequent heating step to activate latent crimp and produce crimped fibers can be disadvantageous in several respects. Utilization of heat, such as hot air, requires continued heating of a fluid medium and therefore increases capital and overall production costs. In addition, variations in process conditions and equipment associated with high temperature processes can also cause variations in loft, basis weight and overall uniformity. Therefore, there is a continuing need for crimped multicomponent fiber nonwoven fabrics having desirable physical attributes or properties such as softness, resiliency, strength, high porosity and overall uniformity. Further, there exists a continued need for efficient and economical methods for making crimped multicomponent fibers without the need for subsequent heating and/or stretching steps.
Accordingly, an object of the present invention is to provide improved crimped multicomponent nonwoven fabrics and methods for making the same. Another object of the present invention is to provide nonwoven fabrics with desirable combinations of physical properties such as softness, resiliency, strength, bulk or fullness, density and/or overall fabric uniformity. Another object of the present invention is to provide such nonwoven fabrics having highly crimped filaments and methods for economically making the same.
The aforesaid needs are fulfilled and the problems experienced by those skilled in the art overcome by a method of making a nonwoven web comprising the steps of: (i) extruding continuous multicomponent fibers having a crimpable cross-sectional configuration, said multicomponent fibers comprising a first component and a second component wherein the first component comprises propylene polymer and the second component comprises a different propylene polymer selected from the group consisting of high melt-flow rate polypropylenes, low polydispersity polypropylenes, amorphous polypropylenes, elastomeric polypropylenes and blends and combinations thereof; (ii) quenching the continuous multicomponent fibers; (iii) melt-attenuating the continuous multicomponent fibers wherein the continuous multicomponent fibers spontaneously develop crimp upon release of the attenuating force; and (iv) depositing the continuous multicomponent fibers onto a forming surface to form a nonwoven web of helically crimped fibers. In an additional aspect, the extruded fibers can be pneumatically melt-attenuated without the application of heat.
In a further aspect, fabrics having excellent physical attributes are provided comprising a bonded nonwoven web of crimped multicomponent fibers having a denier less than about 5, said multicomponent fibers comprising a first component and a second component wherein the first component comprises a propylene polymer and the second component comprises a different propylene polymer selected from the group consisting of high melt-flow rate polypropylenes, low polydispersity polypropylenes, amorphous polypropylenes and elastomeric polypropylenes. In a particular aspect, the first component can comprise an inelastic polypropylene and the second component can comprise an elastomeric polypropylene. In a further aspect, the first component can comprise a substantially crystalline polypropylene and the second component can comprise an amorphous polypropylene. In yet a further aspect, the second component can comprise a propylene polymer having a narrow molecular weight distribution with a polydispersity number less than about 2.5 and the propylene polymer of the first component can have a polydispersity number of about 3 or higher. Additionally, the nonwoven fabric can comprise substantially continuously crimped fibers.